PROJECT SUMMARY Despite recent advances in cancer therapies, platinum-based drugs are still widely used for the treatment of solid tumors. A primary example is cisplatin, which is frequently used to treat lung, bladder, testicular, and cervical cancers. However, limitations of this therapy include the development of drug resistance in cancer cells as well as severe side effects, such as nephrotoxicity and neurotoxicity. One major type of peripheral sensory neurotoxicity is ototoxicity, or drug-induced damage to the inner ear, and cisplatin is the most ototoxic compound that can cause bilateral and irreversible hearing loss. While DNA damage by cisplatin is the major cytotoxic mechanism in cancer cells, cisplatin-induced ototoxicity appears to result from toxic levels of reactive oxygen species and other signaling dysregulation within various cellular compartments. A variety of agents have been tested against cisplatin-induced ototoxicity, mainly based on their antioxidant properties. However, many of them show limited efficacies, and also interfere with the therapeutic effect of cisplatin. In our preliminary studies, we have found that tetrandrine (TET), a compound isolated from the herb Stephanai tetrandra, can protect against noise-induced hearing loss. Previous studies have also revealed that TET can act synergistically with other cancer treatments in several important aspects: increasing tumor cell cytotoxicity, enhancing radiosensitization, reducing multidrug resistance, and inhibiting angiogenesis. At the molecular level, TET can block calcium channels, downregulate multiple drug-resistant proteins, and modulate signaling pathways important for the inflammatory response. Based on these findings, we propose a proof-of-concept project to test whether TET can synergistically work with cisplatin to induce cancer cell death and, at the same time, prevent cisplatin- induced ototoxicity. Because lung cancer is the leading cause of cancer-related death globally, and because cisplatin is widely used to treat this disease, we will be focusing on lung cancer cell lines for this study. We will first study the cytotoxic effects of TET and cisplatin in three lung cancer cell lines and one cochlear cell line, and determine whether TET and cisplatin have synergistic effects when used in combination against these cancer cells while TET has no ototoxic effects on the cochlear cell line (Aim 1). We will then determine whether the TET can prevent cisplatin-induced ototoxicity in vivo while preserving or enhancing anti-tumor efficacy (Aim 2). Our project goal is to develop a new product to combine with cisplatin against lung cancer. This project will generate data important for developing new approaches to reduce cisplatin-induced ototoxicity.